1. Field of Invention
In the manufacture of polyvinyl chloride and copolymers of vinyl chloride, the resin tends to adhere to the reactor walls during the polymerization of the vinyl chloride and comonomers. The buildup of scale on the reactor walls interferes with heat transfer, it consumes valuable monomer which is lost to the final product, and it results in the increase in waste product that must be disposed of safely.
2. Prior Art
U.S. Pat. No. 2,415,252 describes the preparation of phenothiazine derivatives by reacting phenothiazine with formaldehyde and an alcohol under conditions that produce a modified phenothiazine that has attached thereto a methylene group and an alkoxy group. The compounds and their solutions in oil are said to be useful for pharmaceutical, veterinary and pest-control purposes.
U.S. Pat. No. 2,528,092 describes the reaction of phenothiazine with formaldehyde and N-dimethylaniline. The resulting compound is useful as an antioxidant for mineral oil lubricants.
U.S. Pat. No. 4,465,881 describes N,N'-dimers of phenothiazine or a substituted phenothiazine. The compounds result from the linkage of two phenothiazine molecules through their N groups. These dimers are prepared by heating phenothiazine in the presence of an organic peroxide. These dimers are disclosed to be useful to stabilize vinyl aromatic compounds such as styrene and substituted styrenes against undesired polymerization.
U.S. Pat. No. 4,529,500 discloses the use of the N,N'-dimer of phenothiazine or a substituted phenothiazine to protect hydrocarbon processing equipment against fouling during the processing of hydrocarbons at elevated temperatures.
An article published in the USSR by Romanovich and co-authors and reported in Chemical Abstracts as 98:144251d, describes the reaction of phenothiazine and formaldehyde under conditions that favor the production of hardened products wherein reaction appears to take place at the nitrogen group of the phenothiazine, ultimately resulting in the formation of cross-linked products of relatively high molecular weight.
In U.S. Pat. No. 4,229,510, a polymer material is formed from a substituted phenothiazine wherein the nitrogen group is substituted with an alkyl group. It appears that reaction with formaldehyde occurs between the phenyl groups and formaldehyde. The resulting product has the nitrogen group blocked with the alkyl group of the starting material. The resulting products are reported to have photoconductive properties.
U.S. Pat. No. 4,565,834 describes compounds that have the formula of a dimer or polymer of phenothiazine. But, nowhere in the description of the patent is disclosed or suggested compounds or polymers wherein the bridging carbon atom has two hydrogen substituents. The patentees compositions are useful as stabilizer-containing reactive components for the production of polyurethane foams which have little or no tendency toward core decolorization.